1. Field of the Invention
The present invention relates to a plating pretreatment apparatus used when plating treatment is given to the inner peripheral surface of an object to be treated formed into a cylindrical shape such as a cylinder block, and also relates to a plating treatment apparatus used when high-speed plating treatment is given to the inner peripheral surface of an object to be treated formed into a cylindrical shape such as a cylinder block.
2. Description of the Related Art
Usually, before plating is performed, plating pretreatment is done, for example, by electrolytic etching to improve the adhesion of a plating film to a base material. In the pretreatment by means of electrolytic etching, as the condition values of liquid temperature, flow rate, and electric current amount increase, the etching amount increases.
As one example of the conventional electrolytic etching, a method for plating pretreatment in which electrolytic etching is performed in a pretreatment liquid with an aluminum alloy containing silicon being used as an anode has been disclosed in Japanese Patent Provisional Publication No. 11-1795.
However, when pretreatment is given to the inside surface of a cylindrical object to be treated such as a cylinder block, the flow velocity of pretreatment liquid between the cylinder bore inside surface and a cathode is unstable, so that the flow rate, one of the above-described condition values, is nonuniform. Therefore, the etching amount varies depending on the portion to be treated. Further, for a cylinder block for a multi-cylinder engine, the liquid temperature, one of the above-described condition values, is nonuniform between cylinders, so that variations in etching amount occur. The reason for this is that even if the liquid temperature of pretreatment liquid in a pretreatment liquid tank is made constant, the voltage applied to the cylinder block increases the liquid temperature. Also, the reason is that since the outside shape differs between cylinders, a difference in liquid temperature between cylinders arises.
If plating treatment is done in this state, the plating film formed in a portion where the etching amount is small has a lower adhesion than that formed in a portion where the etching amount is large, so that variations in the adhesion of the plating film between portions also occur. Therefore, it has so far been difficult to apply plating pretreatment by means of electrolytic etching to a cylinder block.
On the other hand, usually, when electroplating is given to a cylindrical object to be treated such as a cylinder block, high-speed plating is sometimes given by increasing the current density or by decreasing an anode-cathode distance between the electrode and the object to be treated to enhance the productivity.
First, the case in which the current density is increased will be explained. For example, in the case where SiC is deposited in a form of Nixe2x80x94Pxe2x80x94SiC or Nixe2x80x94SiC as the plating film, if the flow of plating liquid is nonuniform, the deposition of SiC is also nonuniform, so that a problem in regard to wear resistance of the cylinder occurs. Also, at a high current density, abnormal deposition of the plating film called xe2x80x9cburnt depositxe2x80x9d may occur in a portion where the plating liquid flows slowly.
Also, if the anode-cathode distance between the electrode and the object to be treated is short, the flow of plating liquid in a gap between the object to be treated and the anode is liable to be nonuniform, so that a fault of plating film such as burnt deposit develops, and therefore good plating treatment cannot be done. Further, an anode in which soluble nickel pellets are housed in a lath-shaped titanium basket has so far been used. However, since the outer peripheral surface of the anode is formed into a wave shape, the thickness of the plating film formed on the inner peripheral surface of the object to be treated is made nonuniform by the wavy shape of the outer peripheral surface of the anode when the anode-cathode distance is as short as 1 to 5 mm. Therefore, good plating treatment cannot be done.
An adverse influence caused by nonuniform flow of plating liquid arises more easily as the anode-cathode distance, that is, the distance between the anode and the inside surface of the object to be treated is decreased. Therefore, the uniform flow of plating liquid is very important.
One prior art for providing uniform flow of plating liquid has been disclosed in Japanese Patent Publication No. 8-16278. However, this prior art is still insufficient to be used for high-speed plating, and further uniformity of plating liquid flow is demanded. When a multi-cylinder cylinder block is plated, the cylinder is required to have a construction such that it does not interfere with other cylinders.
The present invention has been made to solve the above problems, and accordingly an object thereof is to provide a plating pretreatment apparatus which can etch a cylindrical object to be treated such as a cylinder block uniformly, and can also be used for a multi-cylinder cylinder block uniformly without variations between cylinders, and a plating treatment apparatus which can cause a plating liquid to flow between an anode and an object to be treated, and can also be used for a multi-cylinder cylinder block.
To achieve the above object, the present invention provides a plating pretreatment apparatus in which a cylindrical cathode is disposed in a fixing jig in which a hollow portion is formed, and a cylindrical object to be treated is installed on the fixing jig so that the cathode is arranged in the object to be treated, wherein a lower cathode of the cathode is formed so as to have a smaller diameter than an upper cathode, whereby the volume of a lower void formed between the lower cathode and the fixing jig is made larger than that of an upper void formed between the upper cathode and the object to be treated.
According to the above-described plating pretreatment apparatus, since a plating pretreatment liquid flows at a uniform flow velocity in the object to be treated, uniform etching can be performed over the whole inside surface of the object to be treated, and adhesion of the plating film is improved, resulting in a decrease in poor adhesion.
Also, in the plating pretreatment apparatus in accordance with one mode of the present invention, the cathode is configured so as to be capable of being divided into the upper cathode and lower cathode.
Therefore, when maintenance on the cathode is performed, only the upper cathode or only the lower cathode can be replaced conveniently. Also, pretreatment can be given to a cylinder block with a different bore diameter.
Further, in the plating pretreatment apparatus in accordance with another mode of the present invention, a plurality of hollow portions of the fixing jig and cathodes are provided, and a thermometer is arranged in each cylinder.
Thereby, even in the case of a multi-cylinder engine, the temperature of the pretreatment liquid contained in each cylinder can be grasped, and by appropriately regulating the current value and the flow rate of pretreatment liquid according to the temperature, the liquid temperature can be kept constant. Therefore, there are no variations in etching amount between cylinders, and the adhesion of the plating film is improved, so that the present invention can also be applied to a multi-cylinder cylinder block.
To achieve the above object, the present invention provides a plating treatment apparatus in which a plating liquid is sent from a plating liquid tank into an anode, in which a hollow portion into which the plating liquid is sent is formed, in a state in which an electrical current is caused to flow in a cylindrical object to be treated and the anode, is discharged into the object to be treated through a top end of the anode, is caused to flow between the outside surface of the anode and the inside surface of the object to be treated, is further caused to flow between the outside surface of the anode and the inside surface of an outlet jig, and is returned to the plating liquid tank, whereby the inside surface of the object to be treated is plated, wherein the diameter of a lower anode of the anode, which is disposed in a hollow portion of the outlet jig, is made smaller than the diameter of an upper anode disposed in the object to be treated.
According to the above-described plating treatment apparatus, since an anode-cathode distance between the outside surface of the anode and the inside surface of the outlet jig is made larger than an anode-cathode distance between the outside surface of the anode and the inside surface of the object to be treated, a buffering effect is produced in the outlet jig, so that the plating liquid flows uniformly in the object to be treated. Therefore, when high-speed plating is performed, a fault of plating such as burnt deposit can be restrained, and a shortened treatment time and a reduced treatment cost can be achieved.
The above-described plating treating apparatus preferably has a construction in which the outlet jig, in which a hollow portion is formed, for installing a cylindrical object to be treated on a top face thereof, the cylindrical anode disposed so that the top end thereof projects from the top face of the outlet jig, and the plating liquid tank connected to the anode and the outlet jig through pipes are included, and the cylindrical object to be treated is installed on the top face of the outlet jig and the upper side of the anode is arranged in the object to be treated.
Also, in the plating treatment apparatus in accordance with one mode of the present invention, an insoluble anode is used as the anode.
If the insoluble anode is used, the anode-cathode distance can further be decreased, so that the plating treatment time can further be shortened. For example, when a cylinder block is used as the object to be treated, according to the present invention, the anode-cathode distance can be decreased to 1 to 5 mm, although the conventional anode-cathode distance needs to be 5 mm and larger.
Further, in the plating treatment apparatus in accordance with another mode of the present invention, the anode is configured so as to be capable of being divided into the upper anode and lower anode.
Therefore, when maintenance on the cathode is performed, only the upper cathode or only the lower cathode can be replaced conveniently.
Further, in the plating treatment apparatus in accordance with still another mode of the present invention, a plurality of hollow portions of the outlet jig and anodes are provided, whereby plating treatment can also be given to a multi-cylinder engine.
As described above, according to the plating pretreatment apparatus in accordance with the present invention, a buffering effect is produced by the lower void formed in the fixing jig, so that the plating pretreatment liquid flows uniformly in the object to be treated. Therefore, when high-speed plating is performed, a fault of plating such as burnt deposit can be restrained, and a shortened treatment time and a reduced treatment cost can be achieved.
On the other hand, according to the plating treatment apparatus in accordance with the present invention, a buffering effect is produced in the outlet jig, so that the plating liquid flows uniformly in the object to be treated. Therefore, when high-speed plating is performed, a fault of plating such as burnt deposit can be restrained, and a shortened treatment time and a reduced treatment cost can be achieved.